title: Modification of alternan by dextranase.
abstract: Alternan is a unique glucan with a backbone structure of alternating alpha-(1 --> 6) and alpha-(1 --> 3) linkages. Previously, we isolated strains of Penicillium sp. that modify native, high molecular weight alternan in a novel bioconversion process to a lower molecular weight form with solution viscosity properties similar to those of commercial gum arabic. The mechanism of this modification was unknown. Here, we report that these Penicillium sp. strains secrete dextranase during germination on alternan. Furthermore, alternan is modified in vitro by commercial dextranases, and dextranase-modified alternan appears to be identical to bioconversion-modified alternan. This is surprising, since alternan has long been considered to be resistant to dextranase. Results suggest that native alternan may have localized regions of consecutive alpha-(1 --> 6) linkages that serve as substrates for dextranase. Dextranase treatment of native alternan, particularly with GRAS enzymes, may have practical advantages for the production of modified alternan as a gum arabic substitute.
authors.affiliation: Bioproducts and Biocatalysis Research Unit, National Center for Agricultural Utilization Research, Agricultural Research Service, U.S. Department of Agriculture, 1815 North University Street, Peoria, IL 61604, USA. Tim.Leathers@ARS.USDA.GOV
authors.forename: Timothy D
authors.initials: TD
authors.lastname: Leathers
authors.forename: Melinda S
authors.initials: MS
authors.lastname: Nunnally
authors.forename: Gregory L
authors.initials: GL
authors.lastname: Côté
mesh_terms: D003910:Dextranase / Q000737:chemistry* / Q000378:metabolism*; D004789:Enzyme Activation; D005936:Glucans / Q000737:chemistry* / Q000378:metabolism*; D010407:Penicillium / Q000254:growth & development* / Q000378:metabolism*; D013379:Substrate Specificity
chemical_list: D005936:Glucans; C439358:alternan; D003910:Dextranase